A thermal protector is conventionally known that is embedded in hot air generation device such as a hair dryer, fan heater, a popcorn machine, etc. so as to open and close contacts. Usually, such a thermal protector has, in an integrated manner, a bimetal as a thermally actuated element in order to prevent overheating in the hot air generation device.
Also, for example a flowing air detection switch, an air heater and a hair dryer that use this switch are proposed, wherein the flowing air detection switch forcibly opens the movable contact with respect to the fixed contact when there is no flowing air, independently from the thermal actuation of a bimetal is provided with a movable flowing air blade that makes the movable contact free when receiving a prescribed flow amount of flowing air, causes hot air to flow by driving a heater by bringing the contacts into contact with each other only when flowing air is generated, and blocks a current by opening the contacts through the thermal actuation of the bimetal in response to overheating (See Patent Document 1, for example).
Note that in the sixth embodiment in which the bimetal described by this Patent Document 1 is embedded, it is argued that the portions of the movable contact and the fixed contact are enclosed by an enclosure frame so as to prevent the entering of dust such as powder dust, cotton dust, etc. and thereby contact failure can be prevented as shown in FIG. 14 and FIG. 15.
Incidentally, when for example a hair dryer is set to be used with a current corresponding to the limit of the power source wiring, a large amount of flowing air is necessary in order to set it to blow a heat quantity of for example 1500 W as warm flowing air. In such a case, generally, the cross-sectional area of the air outlet of hair dryers is reduced in order to increase the flow rate.
When such a hair dryer is provided with a thermal protector in it, the thermal protector is usually fixed to a heat-resistant insulation plate such as a mica insulation plate by eyelets etc. through swaging together with Nichrome wire, which is a heat generation body, and is connected electrically to the plate.
Nichrome wire is wound, in a spiral manner, on the outer periphery of a mica insulation plate that is formed in cross directions or hexagonal directions and thereby forms a heat generation unit, and the spiral internal space becomes a flow channel of hot air. The thermal protector is arranged in the flow channel of the hot air and is attached to the mica insulation plate by being directly connected to Nichrome wire in series in wiring.
Incidentally, hair dryers enter an abnormal state in some cases. Examples of such states are an abnormal increase in the internal temperature caused by a decrease in the airflow amount, a case when abnormal heat generation is caused when for example an appliance that can switch voltages for use outside of Japan is used and a mistake occurs in the selection of voltages so that a low voltage is set while the appliance is used with a high voltage, etc.
In such a case, the thermal protector operates so as to block the passage of a current to the Nichrome wire in order to stop heat generation and bring the hair dryer into a safe state. When a thermal protector is attached to a mica insulation plate as described above, a highly effective thermal response is necessary, and accordingly it is provided with the switch structures of a bimetal, a contact, etc. being exposed.
Also, a thermal protector is arranged near the center (root) of the cross directions or the hexagonal directions of a mica insulation plate in order to secure an appropriate insulation distance from the Nichrome wire. When an abnormality such as the above examples occurs and an abnormal temperature is detected in this state, the bimetal is inverted to lift the movable plate so as to open the space between the contacts and block the current.
When for example a high current is flowing upon this blockage of the current, a large breaking arc occurs. Further, because when there is a high current hot air flows in a large flow amount, complicated airstreams are formed by being influenced by the installation positions and installation states of internal components in the hair dryer.
Also, a thermal protector is arranged near the outlet of hot air in many cases although a thermal protector is attached at various positions depending upon the structures of hair dryers etc. The flow rate of air is high in the vicinity of the outlet of hot air as described above.
Because of this, a breaking arc of a high current is often expanded by flowing air from the space between contacts as if it were blown away, depending upon the timing of the occurrence. As a result, a breaking arc having occurred between contacts moves to a conductive portion that is different from a contact, and starts causing damages by due to a high temperature of the arc at a location such as for example the tip of the movable plate.
Further, a breaking arc does not stay in a thermal protector but sometimes files, due to flowing air, from for example the movable contact that instantaneously jumps upon the opening of the contact, to a Nichrome wire that is in the vicinity of the movable contact. This easily occurs when the difference between the potential of a movable plate and the potential of the Nichrome wire is large.